Hydraulic oil

ABSTRACT

1. A HYDROCARBON-BASED HYDRAULIC FLUID COMPRISING A MAJOR AMOUNT OF A HYDROCARBON LUBRICATING OIL HAVING A VISCOSITY OF 100 TO 650 SUS AT 100*F. AND CONTAINING FROM 0.1 TO 15 WEIGHT PERCENT ZINC DI(PRIMARY ISO-OCTYL) DITHIOPHOSPHATE AND FROM 0.03 TO 0.2 PARTS OF A C6 TO C24 ALKENYL SUCCINIC ACID PER WEIGHT PART OF SAID ZINC DITHIOPHOSPHATE; WITH THE PROVISO THAT WHEN THE CONCENTRATION OF SAID ZINC DITHIOPHOSPHATE IS FROM 1.0 TO 1.5 WEIGHT PEERCENT THEN 0.01 TO 1 PART OF A METAL DEACTIVATOR SELECTED FROM TRIARYL OR TRIALKYL PHOSPHATES, ARYL OR ALKYL PHOSPHITES, ALKYLPHENOL SULFIDES, PHOSPHORUS PENTASULFIDE-TERPENE ADDITION PRODUCTS, BENZOTRIAZOLE, PHENOTHIAZINE, BISOCTYL DITHIATHIOPHOSPHATE, PHENYL-1-NAPTHYLAMINE OR MIXTURES THEREOF PER PART OF SAID ZIND DITHIOPHOSPHATE IS PRESENT.

United States Patent O 3,843,542 HYDRAULIC OIL John H. Adams, San Rafael, Califi, assignor to Chevron Research Company, San Francisco, Calif. No Drawing. Filed July 31, 1972, Ser. No. 276,866

Int. Cl. C09k 3/00 US. Cl. 252-75 8 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Each year more and more hydraulic systems are being utilized in industrial, aerospace and mobile applications. The uses vary from enormous hydraulic presses with multi-ton capacities to complex servomechanisms operating under milligram pressures. The hydraulic oils employed in these systems, regardless of the wide divergence of their applications, many times suffer a common problem.

For example, typical problems common to most hydraulic systems include hydraulic oil corrosivity, erosivity, volatility, foaming tendencies, etc. Additives are usually added to the system to ameliorate these and other problems, and their employment has greatly improved the performance and longevity of the hydraulic systems. One type of additive which is particularly important in hydraulic fluids is the corrosion inhibitors or anti-wear agents, typically zinc dialkyl dithiophosphate. These compounds have found widespread commercial success in reducing wear and corrosion in hydraulic systems and are more or less responsible for the increase in machinery life. Although the zinc dialkyl dithiophosphate is quite successful in most hydraulic oils it is burdened with stability problems when exposed to water at elevated temperatures. This instability is commonly referred to as hydrolytic instability.

Although the hydrolytic instability only occurs when water is present, the exclusion of water from the hydraulic oil in most systems is mechanically impossible or at least would require mechanical modifications beyond that considered economically feasible. For example, in almost every hydraulic system an oil reservoir is provided which is vented to the atmosphere. This vent allows breathing of the system during normal thermal contraction and expansion of the hydraulic oil. Air enters into the vented reservoir during thermal contraction and water vapor present in the air condenses on the walls of the reservoir container. The condensate is then free to mix with the hydraulic oil. Water additionally finds access to the hydraulic system through worn or faulty seals, small leaks in connecting heat exchangers, etc.

Thus a need exists for improving the hydrolytic stability of zinc dialkyl dithiophosphates in hydraulic oils that does not detract from or interfere with other necessary properties of the oil and that is relatively easy and inexpensive to produce.

SUMMARY OF THE INVENTION I have found that the anti-wear, oxidation and corrosion inhibiting properties of an hydraulic oil which is exposed to moisture and elevated temperature can be improved by incorporating into a major amount of a lubricating oil from 0.1 to 1.5 weight percent of a zinc di(iso- Patented Oct. 22, 1974 octyl primary) dithiophosphate. The hydrolytic and thermal stability of the zinc dithiophosphate compound can in turn be improved by simultaneously incorporating from 0.03 to 0.2 weight part of a C to C alkenyl succinic acid per weight part of the zinc dithiophosphate into the lubricating oil. The employment of these two components and their concentrations are critical aspects of the practice of this invention. When the zinc di(isooctyl)dithiophosphate concentration is one weight percent or greater, at least one metal deactivator must also be present within the hydraulic oil formulation.

Although the exact mechanism of the combination in exhibiting stable excellent anti-wear and corrosion inhibiting properties under strong hydrolyzing conditions is unknown, it is known that the use of the alkenyl succinic acid with the particular zinc dithiophosphate reduces the corrosion by 10 to 40 fold (as determined by ASTM Hydrolytic Stability Test D2619) over that of the zinc di(iso-octyl)dithiophosphate alone or even over the combination of alkenyl succinic acid with an analog zinc di- (n-octyl dithiophosphate.

DETAILED DESCRIPTION OF THE INVENTION An improved hydraulic fluid is prepared by admixing with a suitable synthetic or petroleum base oil a primary zinc di(iso-octyl)dithiophosphate and an alkenyl succinic acid having from 6 to 24 carbons and preferably from 12 to 16 carbons.

The amount of the Zinc dithiophosphate and alkenyl succinic acid present within the hydraulic oil must be within a narrow range in order to realize the synergism demonstrated in the examples. The zinc dithiophosphate must be present within the range of 0.1 to 1.5 Weight percent and preferably from 0.5 to 1.0 weight percent. The alkenyl succinic acid must be present in an amount from 0.03 to 0.2 weight part and preferably 0.05 to 0.1 weight part per part of zinc di(iso-octyl)dithiophosphate. The concentration of the alkenyl succinic acid present within the hydraulic oil, on the other hand, normally ranges from 0.03 to 0.2 weight percent and preferably from 0.05 to 0.1 weight percent.

When the concentration of the zinc dithiophosphate component is 1 weight percent or greater, a small amount of a metal deactivator must also be present within the hydraulic oil. The amount of metal deactivator employed generally ranges from 0.01 to 1 part per part of zinc dithiophosphate equal to or above about 1 weight percent.

The zinc di(iso-octyl)dithiophosphate component of this invention is commercially available. This compound is usually prepared by reacting primary iso-octyl alcohol with phosphorus pentasulfide to produce the di(primary iso-octyl) dithiophosphoric acid which is thereafter neutralized with a zinc base (oxide, hydroxide or C -C carboxylate) to produce the corresponding Zinc salt.

The alkenyl succinic acid component of this invention is also available commercially. Most of these acids are produced by simply reacting maleic anhydride with an a-olefin and thereafter hydrolyzing the reaction product. Exemplary alkenyl succinic acids include tetrapropenyl succinic acid, butenyl succinic acid, hexapropenyl succinic acid, ndodecenyl succinic-acid, polybutenyl succinic acid, etc.

The base oil which may be employed in the practice of this invention includes a wide variety of natural and synthetic oils such as naphthetic-base paraffin-base, and mixedbase lubricating oils. These oils generally have a viscosity of to 650 SUS (Saybolt Universal Seconds) at 100 F. and preferably from 40 to 70 SUS at a temperature of 210 F. Other base oils include oils derived from coal products and synthetic oils, e.g. alkylene polymers (such as polymers of propylene, butylene, etc., and mixtures thereof), alkylene oxide-type polymers (e.g.,) alkylene oxide polymers prepared by polymerizing alkylene oxide e.g. propylene oxide, etc. in the presence of water or an alcohol, e.g. ethyl alcohol), carboxylic acid esters (e.g., those which were prepared by esterifying such carboxylic acids as adipic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, maleic acid, etc., with alcohols such as butyl alcohol, hexyl alcohol, 2-ethyl-hexyl alcohol, pentaerythtritol, etc.), liquid esters of phosphorus, such as triakyl phosphates (tributyl phosphate, etc.), triaryl phosphates (tricresyl phosphate), alkylaryl phosphates (dibutyl phenyl phosphates, etc.), alkyl benzenes, polyphenols (e.g. biphenyls and terphenyls), alkyl biphenol ethers, polymers of silicon, e.g., tetraethyl silicate, tetraiso propyl silicate, hexyl(4-methyl-2-pentoxy)disilicane, poly(methyl)siloxane, and poly(methylphenol) siloxane, etc. The base oils may be used individually or in combinations, whenever miscible or whatever made so by use of mutual solvents.

Exemplary metal deactivators which may be employed include triaryl or trialkyl phosphates, such as tributyl phosphates, tricresyl phosphate, aryl or alkyl phosphites, alkylphenol sulfides, phosphorus pentasulfide-terpene addition products, benzotriazole, phenothiazin, bis octyl dithiathiadiazole, phenyl-l-naphthylamine, etc., and combinations thereof. Bis octyl dithiathiadiazole has shown very good activity and is a preferred metal deactivator.

In addition to the zinc dithiophosphate and alkenyl sucsinic acid, other additives may be successfully employed within the hydraulc fiuid of this invention without adversely affecting its high hydrolytic stability and performance over a wde temperature scale. One type of additive is a demulsifier which may be employed to prevent water from becoming stably emulsified within the hydraulic oil. Exemplary demulsifiers include petroleum sulfonic acids or salts and particularly the zinc and barium salts thereof, such as zinc lauryl sulfonate, barium dinonylnaphthenic sulfonate, zinc dinonylnaphthenic sulfonate, etc., dimerized unsaturated aliphatic monocarboxylic acids prepared by reacting a monocarboxylic acid with a polyalkylene polyamine followed by reaction with an alkenyl succinic acid anhydride, sulfonated castor oil, etc.

Another additive which may be incorporated into the hydraulic fluid of this invention is a rust inhibitor. Exemplary rust inhibitors include high molecular weight esters such as sorbitan monooleate, butyl stearate, butyl naphthenate, etc., nitrogen compounds, such as amines and amides, metal detergents such as aluminum stearate and lithium stearate, etc.

Another additive which may be employed is an antioxidant. Typical anti-oxidants are organic compounds containing sulfur, phosphrus or nitrogen, such as organic amines, sulfides, hydroxy sulfides, phenols, etc., alone or in combination with metals like zinc, tin or barium. Particularly useful hydraulic fluid antioxidants include phenylalpha-methylamine, bis(alkylphenylamine, N,N-diphenylp phenylenediamine, bis(4-isopropylaminophenyl)ether, N-acyl-p-aminophenol, N-acylphenothiazine, N-hydrocarbylamides or ethylenediamine tetraacetic acid, alkyl phenol-formaldehyde-amine polycondensates, etc.

Other additives which may be employed in the practice of this invention include viscosity index improvers such as polyisobutylenes, polymethacrylates, etc., foam inhibitors, detergents, dispersants, pour point depressants, dyes, odor suppressants, extreme pressure agents and lubricity or oiliness agents.

The concentration of the various components within the hydraulic fluid formulation varies depending upon the properties desired, base oil employed, additives selected, etc. Generally, however, concentration of the various additives will be within the range presented in the followin Table 1.

TABLE 1.HYDRAULIC FLUID Concentration (wt. percent) The following examples are presented to illustrate the practice of specific embodiments of this invention and should not be interpreted as limitations upon the scope of the invention.

EXAMPLES 1-15 These examples are presented to demonstrate the effectiveness of the additive combination of this invention. A series of tests are performed on various hydraulic fluids to determine their hydrolytic stability as measured by ASTM D2619-67, Hydrolytic Stability of Hydraulic Fluids (Beverage Bottle Test Method). In the tests, 75 grams of the hydraulic fluid plus 25 grams of water and a copper test specimen are sealed in a pressure-type beverage bottle. The bottle is rotated, end over end, for 48 hours in an oven maintained at a temperature of 200 F. The weight change of the copper specimen is measured and any decrease in weight is indicative of the hydrolytic instability of the hydraulic oil.

The test fluids employed are formulated from the following base oils or mixtures thereof.

Viscosity at F.

Base oil 'Iypo (SUS) Acid treated Heavy. ..do 200 Citcon-200 Neutral. RPM126 do 126 RPM-480 .do 480 The zinc dithiophosphate additives employed are zinc di(iso-octyl primary)dithiophosphate referred to herein as the iso-octyl ester, zinc di(n-octyl primary) dithiophos phate referred to herein as the n-octyl ester, zinc butyl hexyl dithiophosphate referred to as the butyl hexyl ester and zinc butyl, 1,2-di methylpropyl dithiophosphate referred to herein as the MIBC 1 ester. A conventional zinc sulfonate demulsifier is employed in each test composition at a concentration of 0.05 weight percent unless otherwise stated. The demulsifier is employed to reduce the tendencies of the hydraulic fluid to form a stable emulsion with the water present within the beverage bottle during the test. A conventional polymethacrylate pour point depressant is employed in each test composition at a concentration of 0.75 weight percent in each composition containing the Turbine Oil Stock and at a concentration of 0.35 weight percent in each composition containing Citcon stocks. A conventional silicon oil foam inhibitor is also employed in each test composition at a concentration of 0.002 weight percent. Other additives which are present in some of the tests include tricresyl phosphate (TCP), benzotriazole, tributyl phosphate, and didecyl phenyl phosphite.

The variable components employed and the concentrations of each employed in these tests are shown in the following Table 2 along with the copper weight loss measured in the hydrolytic stability test.

1 MIBC refers to the alcohol employed in making the ester, 1.e. methyl tsobutyl carbinol.

TABLE 2.ASTM HYDROLYTIC STABILITY TEST Addition concentration (weight percent) Components 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Base oil:

Turbine oil:

Light... 35 35 35 35 35 35 35 35 Heavy 65 65 65 65 65 65 65 65 CITCON-ZOO. 25 25 25 25 25 CITCON-350. 75 75 75 75 75 35 35 80 65 65 Zinc dialkyl dithiophosphate:

Isooetyl ester 0.5 1.0 1 0 1 0 1 0 1 0 1.0 10 0 5 n-Octyl ester 1. 0 Butyl-hexylester 1.0 Butyi-MIBC ester 1. 0 Alkenyl succinic acid: Tetrapropenyl succinic acid 0.06 0. 06 0.06 0. 06 0.06 0. 06 0.00 0.06 0.15 0.50 0.01 Other additives:

Tricresyl phosphate 0.1 0.05 0.05 0.05 0.1 0.05 0.05 0.05 0.05 Benzotriazole 0.05 Tributyl nhnsnhata 0. 05 Didecylphenyl phos hite 0. 05 Copper weight loss (mg. 0111. 2.3 7.2 4. 75 0.15 0.24 0.33 0.4 0.52 0.49 2.5 4.2 0.66 2.2 5.15 2.06

The above Table 2 illustrates the synergism of the combination and the required component concentrations.

Thus, a comparison of compositions 1, 2, 11 and (no alkenyl succinic acid) with compositions 4 and 5 (wit-h alkenyl succinic acid) demonstrate a several-fold reduction in copper weight loss. A comparison of composition 6 with composition 10 reveals that the substitution of the n-octyl for the iso-octyl in the zinc dithiophosphate ester octyl)dithiophosphate, 0.06 parts of tetrapropenyl suc- 4 cinic acid, 0.05 parts of tricresyl phosphate and 0.01 parts of his octyl dithiathiadiazole.

It is apparent that many different embodiments of this invention may be made without departing from the scope and spirit thereof; and, therefore, it is not intended to be limited except as indicated in the appended claims.

What is claimed is: 1. A hydrocarbon-based hydraulic fluid comprising a major amount of a hydrocarbon lubricating oil having a viscosity of 100 to 650 SUS at 100 F. and containing from 0.1 to 1.5 weight percent zinc di(primary iso-octyl) dithiophosphate and from 0.03 to 0.2 parts of a C to C alkenyl succ nic acid per weight part of said zinc dithiophosphate; with the proviso that when the concentration of said zinc dithiophosphate is from 1.0 to 1.5 weight percent then 0.01 to 1 part of a metal deactivator selected from triaryl or trialkyl phosphates, aryl or alkyl phosphites, alkylphenol sulfides, phosphorus pentasulfide-terpene addition products, benzotriazole, phenothiazine, bis- 6 octyl dithiathiadiazole, phenyl-l-naphthylamine or mixtures thereof per part of said zinc dithiophosphate is present.

2. The composition defined in Claim 1 wherein a demulsifier is also present in said base oil.

3. The composition defined in Claim 2 wherein said 6 zinc di(primary iso-octyl) dithiophosphate is present in an amount between 1 and 1.5 weight percent and wherein from 0.01 to 1 part per part of said zinc dithiophosphate of a metal deactivator is present in said base oil.

4. The composition defined in Claim 2 wherein said demulsifier is a zinc or barium sulfonate.

5. The composition defined in Claim 2 wherein said alkenyl succinic acid is tetrapropenyl succinic acid.

6. A hydrocarbon-based hydraulic fluid comprising (1) a major amount of a hydrocarbon lubricating oil having a viscosity of 100 to 600 SUS at 100 F.;

(2) from 0.1 to 1.5 weight percent of zinc di(primary iso-octyl) dithiophosphate;

(3) from 0.03 to 0.2 part per part of said zinc dithiophosphate of an alkenyl succinic acid having from 12 to 16 carbon atoms;

(4) from 0.01 to 1 part per part of said zinc dithiophosphate of a metal deactivator when the concentration of said zinc dithiophosphate is from 1 to 1.5 weight percent; and

(5 from 0.01 to 0.1 weight percent of a demulsifier.

7. The composition defined in Claim 6 wherein said alkenyl succinic acid is tetrapropenyl succinic acid.

8. The composition defined in Claim 6 wherein said metal deactivator is tricresyl phosphate, said demulsifier is a barium or zinc sulfonate and wherein a foam inhibitor is also present.

References Cited UNITED STATES PATENTS 2,344,392 3/ 1944 Cook et a1. 25232.7 E 3,184,408 5/ 1965 Wilson et al. 25232.7 E 3,272,744 9/1966 Schallenberg et al. 25232.7 E 3,300,409 1/ 1967 Butler 25232.7 E 3,382,172 5/1968 Lowe 252560 X 3,429,820 2/ 1969 Lyons et al 25278 3,533,943 10/ 1970 Papay 25232.7 E 3,591,497 7/1971 Walker 252 X 3,720,615 3/ 1973 Izumi et al. 252560X LEON D. ROSDOL, Primary Examiner H. A. PIT'LICK, Assistant Examiner U.S. Cl. X.R. 

1. A HYDROCARBON-BASED HYDRAULIC FLUID COMPRISING A MAJOR AMOUNT OF A HYDROCARBON LUBRICATING OIL HAVING A VISCOSITY OF 100 TO 650 SUS AT 100*F. AND CONTAINING FROM 0.1 TO 15 WEIGHT PERCENT ZINC DI(PRIMARY ISO-OCTYL) DITHIOPHOSPHATE AND FROM 0.03 TO 0.2 PARTS OF A C6 TO C24 ALKENYL SUCCINIC ACID PER WEIGHT PART OF SAID ZINC DITHIOPHOSPHATE; WITH THE PROVISO THAT WHEN THE CONCENTRATION OF SAID ZINC DITHIOPHOSPHATE IS FROM 1.0 TO 1.5 WEIGHT PEERCENT THEN 0.01 TO 1 PART OF A METAL DEACTIVATOR SELECTED FROM TRIARYL OR TRIALKYL PHOSPHATES, ARYL OR ALKYL PHOSPHITES, ALKYLPHENOL SULFIDES, PHOSPHORUS PENTASULFIDE-TERPENE ADDITION PRODUCTS, BENZOTRIAZOLE, PHENOTHIAZINE, BISOCTYL DITHIATHIOPHOSPHATE, PHENYL-1-NAPTHYLAMINE OR MIXTURES THEREOF PER PART OF SAID ZIND DITHIOPHOSPHATE IS PRESENT. 